Lifting devices which are mechanically or hydraulically actuated, are used in many different industries for raising and lowering components for assembly operations and the like. There are a number of different lift designs, however, scissor type lifts are one of the most frequently used. Scissor lifts are usually actuated by either hydraulic cylinders or mechanical screw drives.
Hydraulically actuated and/or mechanically actuated scissor lifts are used extensively in the automotive industry, particularly on automotive assembly lines. By way of example only, in this patent, we will describe the anti fall device which is the subject matter of this patent used in association with a mechanically actuated scissor lift.
Vehicles are often assembled on a platform which can be raised or lowered, for the purpose of assembly and mounting of various components onto the vehicle as it progresses down the assembly line. The automotive industry is extremely concerned about safety. An uncontrolled descent of a scissor lift could present a substantial safety hazard to workers that are situated in and around the scissor lift when for example, installing componentry on the vehicle. It is desirable to have safety devices which, upon failure of the drive mechanism of the lift, would prevent uncontrolled descent of the scissor lift platform, in order to minimize and/or prevent injury to personnel.
Currently, the specifications which deal with the safety aspect of scissor lifts include ANSI Specification MH 29.1 Section 8.1.2 which calls for a rate of descent protection, wherein the descent of the lift is promptly arrested or the rate of descent limited to a speed not to exceed the greater of 4 times the normal down speed or 30 feet per minute when fully loaded.
General Motors also have their own internal specification, GMSC 1-99, Section 2.3.13 which calls for an anti fall safety device which senses an over speed condition and arrests the dropping of the scissor lift unit within two inches of travel from the point of detection.
The present invention an anti fall device to be used in association with lifting devices, and particularly mechanical operated scissor lifts, detects catastrophic failure of the drive mechanism and minimizes unwanted descent or uncontrolled rates of descent of the lifts.